1. Field of the Invention
The present invention relates in general to propulsion systems for aircraft which are operable in at least a helicopter mode of flight. The present invention has a particular applicability in the field of tilt rotor aircraft which are operable in either an airplane mode of flight or a helicopter mode of flight.
2. Description of the Prior Art
The control systems for helicopters and tilt rotor aircraft are complex electrical and/or mechanical systems. The control systems respond to the pilot""s input, but also must accommodate forces acting upon rotor assemblies which are generally outside the control of the pilot. Mechanical control systems typically include a swashplate arrangement which consists of a stationary portion and a rotating portion. Typically, the lower, stationary portion is fixed in position and will not rotate, but has the ability to move up and down and/or tilt in any given direction. This is commonly referred to as the xe2x80x9cstationaryxe2x80x9d or xe2x80x9cnonrotatingxe2x80x9d plate. Pilot inputs alter the vertical position of the stationary plate through the collective control and the tilt of the stationary plate through the cyclic control. The rotating portion of the swashplate arrangement is free to rotate. Of course, pilot inputs to the nonrotating portion are passed through to the rotating portion of the control systems.
In the prior art, the rotating portion is typically connected mechanically to each individual rotor blade. For example, in one type of control system, pitch links are connected to pitch horns which are carried by the rotor blade, thus allowing the rotating plate to alter the blade angle of each rotor blade. However, it is necessary to include in control systems a subsystem which reduces the degree of flapping as much as possible. In the prior art, there are two basic approaches: one is to utilize a delta-3 hinge; the other is to utilize offset pitch horns. In tilt rotor aircraft, it is especially important to counteract the detrimental effects of flapping, especially because the aircraft is capable of very high speed travel, particularly in the airplane mode of flight.
The present invention is directed to an improved control system which may be utilized in a helicopter aircraft or a tilt rotor aircraft which provides better control of flapping than can be obtained with the prior art.
It is one object of the present invention to provide optimized control over flapping even though the physical configuration of the rotor blades and/or control connections between the rotating and nonrotating portions of the control system are in less than optimum locations.
It is another object of the present invention to provide a mechanical or electromechanical feedback input subsystem which provides a mechanical input to the control system or swashplate assembly which compensates for a less than optimum delta-3 coupling between the rotating and nonrotating portions of a control system.
These and other objects and advantages are achieved as is now described. In one particular embodiment of the present invention, an improved aircraft with tilt rotor assembly is provided. It includes a craft body and a plurality of rotor blades which are subject to three modes of flight operation. In an airplane mode of flight the plurality of rotor blades are in a position which is transverse to the craft body. In a helicopter mode of flight the plurality of rotor blades are in a rotor position which are substantially parallel to the craft body. In a helicopter mode of flight, the direction of flight is controlled by a rotor thrust vector. The aircraft is capable of making an in-flight transition between the airplane mode of flight and the helicopter mode of flight. In this transition mode, the plurality of rotor blades are moved between the rotor disk positions associated with the airplane mode of flight and the helicopter mode of flight. In the preferred embodiment, a tilting mast is utilized to transition between the airplane mode of flight and the helicopter mode of flight. The tilting mast couples the plurality of rotor blades to the craft body and is under the control of systems which allow for the selective moving of the plurality of rotor blades between the three modes of flight. Preferably, a hub is provided for coupling the plurality of rotor blades to the tilting mast in a manner which transfers torque and thrust while allowing tilting of the rotor thrust vector.
A main swashplate is provided for tilting in response to pilot inputs to control the direction of the rotor thrust vector. A plurality of pitch horns are provided. Each pitch horn is mechanically coupled to a particular one of the rotor blades and to the swashplate. The pitch horns communicate swashplate inputs to each of the plurality of rotor blades. This allows the pilot inputs to be passed from the nonrotating portion of the control assembly to the rotating portion of the control assembly. Links are provided which connect the plurality of pitch horns to the main swashplate.
In the present invention, each of the plurality of pitch links is mechanically coupled to a particular one of the plurality of rotor blades by one of the plurality of pitch horns in a particular position which yields a xe2x80x9cdelta-3xe2x80x9d value which is not optimum. A feedback swashplate and cooperating feedback links are provided for receiving disk tilting inputs from a plurality of rotor blades during flight, and for supplying a mechanical input to the main swashplate to compensate for the less than optimum delta-3 coupling between the plurality of pitch horns and the plurality of links.
An alternative embodiment of the present invention allows for compensation for less than optimum delta-3 coupling in an electromechanical control system which utilizes controllable actuators to provide the mechanical coupling between the rotor blades and the swashplate. The controllable actuators may comprise electrically controllable actuators, hydraulic actuators, or electro-hydraulic actuators.
Additionally, the present invention has comparable utility in conventional helicopter aircraft and may be utilized in either mechanical control systems or electromechanical control systems.
The above as well as additional objects, features, and advantages will become apparent in the following description.